CZ2022248A3 - A method of producing nanofibers by alternating electrospinning, a device for carrying out this method and a device for the production of a nanofiber thread - Google Patents

Abstract

In the method of producing nanofibers by alternating electric spinning of a polymer solution or melt on the spinning electrode (1), the nanofibers (5) are formed from the polymer solution or polymer melt in the spinning area (10) formed on the spinning electrode (1) and are carried away from it by the action of the electric wind . In the spinning region (10), a narrow planar linear polymer solution is formed, which has a finite length and is open in the spinning direction, and in the central part of the spinning region (10), a supercritical electric field intensity (E) is created along the length of the spinning region (10) , during which nanofibers (5) are created, moving from the spinning region (10) in a planar formation, where they gradually lose their kinetic energy, and in a place with zero kinetic energy, nanofibers (5) form a linear virtual collector (7) for stopping, collecting and the compaction of the nanofibers (5) into a linear nanofiber formation, the so-called ribbon (6) of nanofibers, which is pulled away. The solution also relates to a device for carrying out the method and a device for the production of a nanofibrous thread.

Description

A method of producing nanofibers by alternating electrospinning, a device for carrying out this method and a device for the production of a nanofiber thread

Field of technology

The invention relates to a method of producing nanofibers by alternating electric spinning of a polymer solution or melt on a spinning electrode, in which nanofibers are formed from a polymer solution or polymer melt in a spinning region created on a spinning electrode and are carried away from the spinning region by the action of electric wind.

The invention also relates to a device for the production of nanofibers by alternating electrical spinning of a polymer solution or melt, in which a spinning region is formed on a spinning electrode connected to a source of alternating electrical voltage.

Current state of the art

In the preparation of nanofibrous threads, oriented and twisted nanofibers are the basis for their construction. Currently, a number of methods have been developed in the field of electrospinning to obtain oriented and twisted bundles of nanofibers, which can be attributed to two main aspects: obtaining ordered nanofibers by improving the collection device or adding an auxiliary electrode.

CN111118677 describes the production of nanofibrous yarn by electrospinning. The device includes a cylindrical collector, which consists of a cavity and a neck rotatable about its axis, the diameter of the upper opening of the neck being smaller than the diameter of the lower opening of the cavity. Inside the bottom opening of the cavity is placed an electrostatic rotating spinning electrode connected to a high voltage source, into which the spinning solution is fed. In the upper part of the collector cavity, compressed air inlets open into its interior, and a counter electrode is arranged above them, which can be grounded or connected to a voltage source with the opposite polarity to the rotating spinning electrode.

The nanofibers created on the rotating spinning electrode are carried by the action of the electrostatic field to the counter electrode, and by the action of the air current, they are carried up into the neck of the cylindrical collector, which rotates due to its rotation and the supplied air current, an air vortex is created, which twists the nanofibers into a yarn, which is further removed and wound on a spool.

The nanofibers are twisted immediately after their formation due to the rotation of the spinning electrode and the subsequent action of the air vortex, so that they do not parallelize before they are twisted, the twisting takes place unevenly and, as a result, the strength and appearance are variable.

CN111286792 describes a horizontal arrangement of an electrospinning device comprising a rotating jet spinning electrode and a collection electrode formed by a hollow cylinder coaxially arranged against it, with a DC electric field between the spinning and collection electrodes. At least two air jets directed towards the axis of the collecting electrode are arranged around the rotating jet spinning electrode. Due to the electric wind, the nanofibers created by the rotating jet spinning electrode are carried to the hollow cylinder forming the collection electrode, and as a result of the rotation of the jet spinning electrode and air currents from the nozzles, they are twisted into a yarn, which, after passing through the cavity of the collection electrode, is pulled out and wound on a spool.

Even with this solution, the aim is to twist the nanofibers as soon as possible after their formation without achieving their parallelization.

- 1 CZ 2022 - 248 A3

In both cases, the disadvantage of the electrostatic production of nanofiber yarn is the low cohesion of the yarn, the irregularity of the twists and the bad orientation of the nanofibers.

Currently, a method for the continuous preparation of nanofiber yarns is known, for example from CN110644080, in which the nanofibers are created from a polymer solution in a jet head, from which the nanofibers are pulled away by the action of a high-speed air stream created in a venturi tube and enter the venturi collection tube through a funnel-shaped collection tube system, where they are straightened and oriented into oriented bundles of nanofibers using vacuum adsorption in a Venturi collection system. Oriented bundles of nanofibers are subsequently twisted and agglomerated by the twisting device into a nanofiber yarn, which is wound on a spool in the next step. The twisting device includes air nozzles for supplying air currents in a tangential direction to the twisted yarn.

From the point of view of the subsequent processing and use of nanofiber yarns, it is not enough to meet the current requirements for their preparation, only to obtain oriented fibers, but it is necessary to be able to obtain oriented fibers or fiber bundles continuously and uniformly apply a certain degree of twist to them in order to ensure the length and degree of orientation of the fibers in nanofibrous yarn. Existing electrospinning technologies for the continuous production of nanofibrous yarns have a low yield and low quality of the produced nanofibrous yarns.

From EP2913951 B1, a method for the production of polymer nanofibers is known, in which the polymer nanofibers are formed by forcefully applying an electric field to a polymer solution or melt located on the surface of a spinning electrode, the electric field for spinning being alternately created between the spinning electrode to which supplies an alternating voltage, and air and/or gas ions created and/or supplied to its surroundings, without a collecting electrode, while depending on the phase of the alternating voltage on the spinning electrode, polymer nanofibers with the opposite electric charge and/or with sections with the opposite electric charge are created, which, after their formation due to the action of electrostatic forces, cluster into a linear formation in the form of a bag or a strip, which moves freely in space in the direction of the gradient of the electric fields away from the spinning electrode.

Spinning by the alternating high voltage method is another way to produce nanofibers, an alternative to electrostatic spinning. However, its yield is still not at such a level that pure nanofibrous yarn can be produced using this method. Therefore, according to EP3303666, a method of producing a core yarn with a sheath of polymer nanofibers enveloping the supporting linear structure forming the core during its passage through the spinning chamber was proposed, in which a spinning electrode connected to the supply of a polymer solution and powered by alternating high voltage is arranged under the supporting linear structure, at the head of which is in the spinning space in the immediate vicinity of the face of the spinning electrode and nanofibers are formed above it, while the supporting linear structure rotates in the spinning space around its own axis. Nanofibers are formed around the face of the spinning electrode and are formed in the spinning space into a hollow electrically neutral nanofiber tow, in which the nanofibers are arranged in an irregular lattice structure, in which the nanofibers change their direction in short sections, while the hollow electrically neutral nanofiber tow with the effect of electric of the wind drifts towards the support linear structure and turns into a flat belt that is brought to the periphery of the support linear structure, the belt formed from the hollow electrically neutral nanofibrous plume wraps around the rotating and/or ballooning support linear structure in a helix shape and forms a nanofiber sheath on it , in which the nanofibers are arranged in an irregular lattice structure, in which the individual nanofibers change their direction in short sections.

The nanofibrous tow represents an ideal material for the sheath of the core yarn, because due to its electrical neutrality and irregular lattice structure, in which the individual nanofibers change their direction in short sections, it is able to form a solid sheath enveloping the core of the yarn and not touching its surroundings during winding and coiling, and subsequent unwinding during processing. However, if a purely nanofibrous yarn were to be produced from the nanofibrous tow, there would be a problem with insufficient

- 2 CZ 2022 - 248 A3 by the amount of nanofibers and further with the grid structure of the plume, which does not allow parallelization of the nanofibers.

At present, there is no satisfactory method of producing nanofibrous yarn with the potential for industrial application. Low productivity, reliability and a limited selection of materials prevent the current methods of nanofiber yarn preparation from being applied. Their production is carried out as part of research work only on a laboratory scale.

Classic yarn with a permanent twist is produced, for example, on ring or rotor spinning machines, where a ribbon of parallel fibers is first formed and then this ribbon is twisted, creating a yarn with high tensile strength and uniform twist. However, it is not yet possible to create yarn from nanofibers in this way.

The aim of the invention is to propose a method of producing nanofibers by alternating electrospinning of a polymer solution or melt, in which nanofibers would be produced in sufficient quantity and carried away from the spinning area in such a way as to form a ribbon of nanofibers in a certain place, in which the nanofibers would be at least partially parallelized, while should have sufficient strength to allow them to be pulled off and wound on a coil for subsequent use or processing into textile formations using known textile technologies.

At the same time, the aim of the invention is to create a device for carrying out such a method and a device for the production of nanofibrous yarn.

The essence of the invention

The aim of the invention is achieved by a method of producing nanofibers from a polymer solution or melt in an alternating electric field on a spinning electrode, in which nanofibers are created from a polymer solution or polymer melt in the spinning region formed on the spinning electrode and are carried away from it by the action of electric wind, while the essence of the invention consists in the fact that in the spinning region a narrow, planar linear structure of the polymer solution is formed, which has a finite length and is open in the direction of spinning, and creates a supercritical electric field intensity, at which the nanofibers created from the spinning region move in a planar structure in which gradually losing its kinetic energy, and at a point with zero kinetic energy, the nanofibers form a linear virtual collector, in which the nanofibers stop, collect and compact into a linear nanofiber formation, the so-called nanofiber ribbon, which pulls away. Due to the high surface area of the nanofibers and the binding forces between the individual nanofibers, the nanofiber ribbon created in this way has sufficient cohesion, which enables it to be wound on a spool for further technological operations, such as twisting, elongation, thermal fixation, etc. By twisting, a nanofiber ribbon is created .

A virtual collector is formed at the point of force balance of electric and gravitational forces acting on the formed nanofibers. Gravitational forces are caused by the weight of the nanofibers, and electric forces represent the sum of all electric forces acting on the nanofibers, i.e. the electric wind force from the spinning electrode, the electric wind force from other charged parts of the spinning device, the force from ionized air ions and the force from oppositely charged parts of nanofibers formed in the preceding half-wave of an alternating electric field.

According to one alternative embodiment of the invention, the spinning region is straight and the nanofibers emerging from it move in a planar planar structure whose thickness corresponds to the width of the spinning region and whose length corresponds to the length of the spinning region.

For the production of a larger amount of nanofibers, in another alternative of this embodiment, a double spinning region can be created by increasing the width of the spinning electrode, while the nanofibers coming from both spinning regions move in planar surface formations, which in

- 3 CZ 2022 - 248 A3 of the direction of movement of the nanofibers move away from each other. In this way, two ribbons of nanofibers are formed on one spinning electrode, which can be further processed separately or combined before processing.

In another alternative embodiment of the invention, the spinning area is formed by a part of a circle on the circumference of the disk spinning electrode, and the nanofibers emerging from it move in a planar plane perpendicular to the axis of rotation of the disk spinning electrode, while the linear virtual collector is formed by a part of the circle.

Even in this embodiment, for the production of a larger number of nanofibers, the width of the spinning electrode can be increased and a doubled spinning region can be created on it, while the nanofibers coming from both spinning regions move in conical flat formations that move away from each other in the direction of movement of the nanofibers until virtual collectors are formed , where it creates two ribbons of nanofibers that can be further processed separately or combined before further processing.

In all the described embodiments, the formed ribbon of nanofibers is wound on a spool, being capable of unwinding and further processing.

In order to speed up the production process, according to another alternative embodiment of the invention, a twist can be given to the ribbon of nanofibers before it is wound, thereby creating a nanofiber thread. At the same time, the turn can be granted false or permanent.

The essence of the device for the production of nanofibers by alternating electrospinning for the production of a ribbon of nanofibers is that a flat linear structure of a polymer solution or polymer melt is placed on the spinning area of the spinning electrode, which has a finite length and is open in the direction of spinning, i.e. the direction of the maximum gradient of electric field, while the intensity of the electric field in the spinning area along its length is set to a supercritical value, at which nanofibers are created, which are carried in the direction of the maximum gradient of the electric field in a planar formation into a linear virtual collector, where they are stopped and compacted into a ribbon of nanofibers , which is introduced into the towing and winding device.

At the same time, according to one alternative embodiment, the fiberization region can be straight, with the maximum gradient of the electric field pointing vertically upwards, so that the formed nanofibers are carried vertically upwards to the virtual collector.

At the same time, the spinning electrode can be formed by a strip spinning electrode, or a linear spinning electrode formed by a linear flexible structure, for example a string, a thin tape, or a thin strap, on which the polymer solution is only on the spinning area.

If the linear flexible structure forming the spinning electrode is composed of several interlaced or intertwined parts, a shielding bar is placed under the spinning area, which can also cover the edges of the linear flexible structure, so that spinning takes place only on its upper side, open in the spinning direction.

By increasing the width of the linear flexible structure forming the linear spinning electrode and by suitably setting the intensity of the electric field, the creation of two spinning regions near the edges of the linear flexible structure is achieved. These spinning regions can be formed by protrusions on the edges of the belt, or the edge of the belt.

In another alternative device, the spinning electrode is formed by a narrow rotating disk spinning electrode, which with the lower part of its circumference extends into the polymer solution or melt in the tank, and on the free part of the disk spinning electrode circuit, a spinning area is formed, which is formed by a part of a circle, while the maximum gradient of electric field points from

- 4 CZ 2022 - 248 A3 spinning regions in the radial direction and the nanofibers are entrained in a planar surface formation, from which a ribbon of nanofibers is formed in the virtual collector.

To increase the amount of nanofibers produced, the rotating disk spinning electrode is mounted on a common shaft with at least one other rotating disk spinning electrode.

An increase in the amount of nanofibers produced can also be achieved by arranging several rotating disc spinning electrodes in a row.

In another embodiment, the rotating disk spinning electrode has a larger disk width, so two spinning regions are formed on its edges, which are formed by a part of a circle, and the maximum gradient of the electric field creates conical surface formations on the edges of the disk spinning electrode, in which the nanofibers are carried into virtual collectors , in which a ribbon of fibers is formed, with the conical planar formations of the nanofibers moving away from each other to form a "V" in cross-section.

According to another alternative embodiment, the spinning electrode is made up of an overflow spinning electrode, the device comprising a reservoir of polymer solution in which a supply of polymer solution is vertically placed, at the upper end of which an overflow electrode is arranged, while the supply opens on its upper face and around its mouth an overflow surface is created that slopes slightly from the inlet of the polymer solution to the edge of the overflow electrode and ends with a peripheral edge that forms the spinning region of the overflow spinning electrode, on which the nanofibers are elongated, which are carried by the electric wind in the direction of the maximum gradient of the electric field through the spinning space in the radial direction from the peripheral edge of the overflow electrode and are collected at the point of the virtual collector, where they are compacted into a mass forming a ribbon of nanofibers, which is pulled from the virtual collector in a tangential direction to the virtual collector and further wound into a coil or processed into a thread.

The created ribbon of nanofibers is taken from any of the above-mentioned spinning devices to a device for the production of nanofiber thread, which contains a twisting means for creating a false or permanent twist, and then it is guided to a winding device and wound on a spool.

Clarification of drawings

The invention will be further described on the basis of the attached drawings, where Fig. 1a distribution of electric field intensity around the peripheral part of a narrow rotating disk electrode for creating nanofibers for conventional spinning, Fig. 1b distribution of the electric field intensity around the peripheral part of the narrow rotating disk electrode for the formation of nanofibers for the production of a ribbon of nanofibers, Fig. 1c distribution of electric field intensity on a rotating disc electrode with a recess in the middle of its circumference, Fig. 2a diagram of the effect of the maximum gradient of the electric field on the circumference of the narrow rotating spinning electrode, Fig. 2b, diagram of the effect of the maximum gradient of the electric field on the wider rotating spinning electrode, Fig. 2c diagram of the effect of the maximum gradient of the electric field on a rotating spinning electrode with a circumferential recess, Fig. 3 diagram of the production of nanofibers on a narrow rotating disk spinning electrode for the production of a ribbon of nanofibers, Fig. 4 diagram of the production of nanofibers on a wider rotating disk spinning electrode for the production of two ribbons of nanofibers from one peripheral surface, Fig. 5 diagram of the production of nanofibers on a pair of narrow rotating disk spinning electrodes for the production of two ribbons of nanofibers, Fig. 6a diagram of the arrangement of three disc spinning electrodes in a row in elevation, Fig. 6b diagram of the arrangement of three disk spinning electrodes in plan view, Fig. 7a is a diagram of the production of nanofibers for a ribbon of nanofibers on a belt spinning electrode in a side view, 7b is a diagram of the production of nanofibers for a ribbon of nanofibers on a belt spinning electrode in elevation, Fig. 8a is a diagram of the production of nanofibers for the production of a ribbon of nanofibers on a cross-sectional electrode, Fig. 8b view of the production of nanofibers on the overflow electrode according to Fig. 8a, Fig. 9a is a diagram of the production of nanofibers for the production of a ribbon of nanofibers on a linear spinning electrode in section A-A from Fig. 9b, which shows this arrangement in a front view, Fig. 9c shows detail A from Fig. 9a, on which is linear

- 5 CZ 2022 - 248 A3 spinning electrode with applied polymer solution and shielding strip, Fig. 10a, 10b a diagram of the production of nanofibers according to Fig. 9a, 9b with one reservoir of polymer solution, Fig. 11 section of a linear spinning electrode formed by a strip with a recess in the central part, Fig. 12 a section of a linear spinning electrode formed by a flat strip and Fig. 13 shows a diagram of a device for the production of a nanofibrous thread from a ribbon of nanofibers.

Examples of implementation of the invention

The method of producing nanofibers by alternating electrospinning of a polymer solution or melt will be described below. Since polymer melt spinning proceeds in the same way as polymer solution spinning, only polymer solution spinning will be described in the following.

For the production of nanofibers from a polymer solution to create a ribbon of nanofibers, the technology of spinning in an alternating electric field is used, which is created by an alternating voltage with an amplitude of, for example, 25 to 50 kV, depending on the geometry and arrangement of the spinning electrode 1 at a frequency of, for example, 10 to 1000 Hz. The polymer solution usually consists of a solution of PVB, PCL, PVA, or other spinnable solutions

During ordinary spinning in an alternating electric field, the aim is to produce the largest possible number of nanofibers per unit of time, which are created over the entire working surface of the spinning electrode and are carried away from the spinning electrode by the electric wind or by auxiliary air currents to the collector, which is neither grounded nor connected to the source of electrical voltage and which can be, for example, a flat textile or a linear fiber formation, which after being wrapped with a nanofiber coating forms a core composite nanofiber yarn. The formation of nanofibers begins at a critical value of the electric field intensity, which is different depending on the type of polymer solution being spun, the value of the voltage, the quality of the gas in the spinning chamber, and other parameters. At a lower value of the electric field intensity than the critical one, nanofibers are not formed, or their formation ceases. Therefore, during ordinary spinning in an alternating electric field, using a specific design of the spinning electrode, a higher electric field intensity than the critical one, i.e. supercritical, is used, which creates a high-intensity electric field on the spinning electrode in order to eliminate the risk of interruption of the spinning process, to ensure sufficient evaporation of the solvent and a sufficiently strong electric wind is provided to transport the nanofibers to the collector.

The distribution of the supercritical intensity E of the electric field for the aforementioned conventional spinning of the polymer solution Z on the narrow rotating disc spinning electrode 11 is shown in Fig. 1a for a disk diameter of 300 mm, a disk thickness of 1 mm, a polymer solution layer thickness of 0.2 mm, and a voltage amplitude of 50 kV. The supercritical value of the electric field intensity E for the PVB polymer solution is equal to or greater than 3000 V/mm ² . It is clear from the figure that the supercritical value of the intensity E of the electric field is reached in a wide area around the peripheral part of the disk. Spinning of the polymer solution Z therefore takes place on the entire peripheral surface of the disc and on the part of the disc faces near the disc circumference, and the created nanofibers are carried through the spinning space to the surface of the collector (not shown).

In order to achieve the formation of nanofibers 5 by alternating electrospinning of the Z polymer solution for the production of the ribbon 6 of nanofibers according to the invention, a narrow spinning area 10 covered with the Z polymer solution, which has a finite length and is open in the spinning direction, must be formed on the spinning electrode 1. The spinning area 10 can be straight, for example in the case of a strip, tape or cable spinning electrode, or it can be formed by a part of a circle, for example in the case of a rotating disc spinning electrode 11. At the same time, the alternating electric power supply of the spinning electrode must be set to a value at which the supercritical the intensity E of the electric field on the narrow spinning region 10 creates the relevant spinning electrode 1 especially above its central part, so that spinning takes place dominantly in the central part of this spinning region 10.

- 6 CZ 2022 - 248 A3

This is achieved in an exemplary embodiment by distributing the supercritical intensity E of the electric field for spinning the polymer solution Z on the narrow rotating disk spinning electrode 11, which is shown in Fig. 1b for a disk diameter of 300 mm, a disk thickness of 1 mm, a polymer solution layer thickness of 0.2 mm and a voltage amplitude of 30 kV. Compared to the previous design intended for conventional spinning, with a reduction in the voltage amplitude, the area of supercritical intensity E has significantly decreased and is only above the middle part of the peripheral surface of the disc. All the nanofibers 5 created are created above the central part of the peripheral surface of the disc and are carried away from the rotating disc spinning electrode 11 in a planar surface formation that is perpendicular to the axis of rotation of the disc. The nanofibers 5 stop at the same distance from the spinning electrode 11, in the place of the so-called virtual collector 7, and are not carried further.

This generally means that Taylor cones begin to form on the surface of the polymer solution Z in the narrow spinning region 10 of the spinning electrode 1, from which, due to the effect of a sufficiently strong electric field, nanofibers 5 begin to elongate, which are carried away from the spinning region of the spinning electrode in the direction of the electric wind of the maximum values of the gradient of the electric field, i.e. in the plane of the greatest density of electric field lines, in one area, while in the area where the repeated natural slowing down to stopping of the nanofibers occurs, a virtual collector 7 is formed, i.e. the place where the nanofibers are collected and compacted and thus create a ribbon 6 of nanofibers, and this ribbon 6 is pulled away. As a result of the periodic change in the polarity of the power supply of the spinning electrode 1, the created nanofibers 5 in the area of the virtual collector 7 are compacted into a material structure due to the loss of speed. Since these nanofibers 5 are formed in one flat structure, a linear structure called a ribbon 6 of nanofibers is created due to this compaction. The flat formation of nanofibers has a thickness corresponding to the width of the spinning area, which is narrow and its width varies in the interval of up to 5 mm. The length of the virtual collector 7 corresponds to the length of the spinning area 10 on the spinning electrode 1.

If the spinning takes place in a vertical plane as described above, the sheet formation of the nanofibers 5 is planar because all the forces acting on it act in the vertical direction.

If the spinning takes place in a plane inclined from the vertical plane, for example on both edges of strip or tape electrodes, nanofibers 5 are created in the direction of the maximum values of the electric field gradient, i.e. in a plane inclined from the vertical plane, but by the action of gravitational forces and mutual repulsive forces of nanofibers with the same charge, the nanowires 5 are deflected so that a virtual collector 7 is formed under the surface of the electric field gradient.

If the spinning takes place by creating nanofibers in a conical surface, for example, on both edges of the wide rotating disc spinning electrode 11, the nanofibers 5 are created in the direction of the maximum values of the electric field gradient. The distribution of regions of electric field intensity E is shown in Fig. 1c on a wide rotating disc spinning electrode 11, with a width of, for example, 6 mm, on the circumference of which a recess 111 is formed in the middle, which creates protrusions 112 on the edges of the circumference of the disc spinning electrode, on which the supercritical intensity E of the electric field is concentrated. This creates two spinning regions 110, one on each projection 112. Due to the distribution of the supercritical intensity E, the nanofibers 5 in this embodiment are carried in two conical flat formations that move away from each other in the direction of movement of the nanofibers 5. The distance is also helped by the fact that the nanofibers 5 formed on both protrusions 112 of one disk spinning electrode 11 have the same residual electrical potential at a specific time, so they repel each other. In addition, the gravitational force acts on the nanofibers, which deforms the conical surface formations, so that the virtual collector 7 is formed under the surface of the electric field gradient.

For the rotating disk spinning electrode 11 without a peripheral recess, the supercritical intensity E of the electric field will be concentrated at the edges of the peripheral surface of the disk, so that the nanofibers 5 will be formed as described above. It will only be necessary to set the voltage amplitude more precisely in order to create an electric field with a supercritical intensity E in the region of the edges of the peripheral surface of the disc.

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The virtual collector 7, i.e. the place with the density concentration of the nanofibers 5, is formed at the point of force balance of all electric and gravitational forces acting on the created nanofibers 5. The electric forces represent the sum of all the electric forces acting on the nanofibers 5, i.e. the force of the electric wind from the spinning electrode 1, the force of the electric wind from other charged parts of the spinning device, the force from ionized air ions and the attractive force from the oppositely charged parts of the nanofibers 5 created in the previous half-wave of the alternating electric field, as well as the repulsive force from the positively charged parts of the nanofibers 5. The virtual collector 7 means a narrow area terminating the surface formation of the created nanofibers 5, where the created nanofibers 5 lose their movement speed when moving from the spinning area 10 of the spinning electrode 1. The reason for their slowing down is the reversal of the polarity of the spinning electrode 1 in the second half of the period of the supplied alternating electric voltage. The already formed nanofibers 5 carried to the virtual collector 7, or the nanofibers 5 collected in the virtual collector 7, remain with a residual electric charge of the polarity of the previous half-wave electric voltage, so that they are now oppositely charged with respect to the current polarity of the spinning electrode 1. In this way, an electric potential difference is created required for the initialization and progress of the AC spinning process. When starting the spinning process, an electric potential is created between the polymer solution Z in the spinning area 10 of the spinning electrode 1 and the air ions in the vicinity of the spinning electrode 1.

The slowing down to stopping of the nanofibers in the area of the virtual collector 7 is determined by changing the polarity of the supplied electric voltage, while the distance of the virtual collector 7 from the spinning area 10 of the spinning electrode 1 is determined by the frequency of the supplied electric voltage. A suitable configuration of the spinning electrode 1 and a suitable setting of the amplitude, frequency and shape of the supplied electrical signal enables the creation of a linear ribbon 6 of nanofibers and its uniform continuous withdrawal outside the spinning space 41 for further operations. The position of the virtual collector 7, i.e. the place where the ribbon 6 of nanofibers is formed, is mainly determined by the frequency and amplitude of the supplied electric voltage. The stable formation of the ribbon of 6 nanofibers is ensured by the creation of a force balance of all electrical, mechanical and gravitational forces acting on the ribbon of 6 nanofibers in an alternating electric field. The amount of created nanofibers 5 and thus the weight of the ribbon 6 of nanofibers depends on the configuration of the spinning electrode 1, on the value of the intensity E of the electric field and the size of the spinning area 10, i.e. the surface of the spinning electrode 1, on which this intensity E is achieved, i.e. on the value of the amplitude of the supplied alternating electric Tension. With the balance of electrical, gravitational and mechanical forces, the weight of the ribbon of 6 nanofibers is ensured by the withdrawal speed, which can be regulated according to technological requirements.

An important element of creating a ribbon of 6 nanofibers is the course of the applied alternating electric voltage. For a more stable formation of the ribbon 6 nanofibers, it is advantageous to shorten the time of the transition region between the positive and negative half-wave of the electric voltage, so it is most advantageous to use a rectangular or at least a trapezoidal course of the electric voltage, when the transition regions are shorter and the production process is therefore more stable. In the case of a rectangular waveform of the electric voltage, the magnitude of the intensity E of the electric field in the respective half-wave is constant, in the case of a sinusoidal waveform it changes.

The fundamental advantage of the proposed method of manufacturing nanofibers for the creation of the ribbon 6 of nanofibers is the homogeneity of the ribbon 6 of nanofibers, because the creation of the ribbon 6 of nanofibers in the virtual collector 7 is not affected by any frictional forces that would affect the homogeneity. The homogeneity of the created ribbon 6 of nanofibers is ensured by invariance over time and a sufficient amount of Taylor cones on the surface of the polymer solution in the spinning region 10 of the spinning electrode 1, from which nanofibers 5 are formed due to the effect of an alternating electric field. of the spinning area, the number of Taylor cones is constant, which leads to the creation of a constant amount of nanofibers 5 and thus to the achievement of a uniform ribbon of 6 nanofibers.

The ribbon 6 of nanofibers holds together due to the high specific surface area of the nanofibers 5 and the intermolecular binding forces between individual touching nanofibers 5. Another reason is the natural entanglement of the positively and negatively charged sections of the nanofibers 5 in the region of the virtual collector 7. The cohesion of the ribbon 6 of nanofibers allows it to be wound on a coil for the next

- 8 CZ 2022 - 248 A3 technological operations, such as twisting, stretching, heat fixation, etc. By twisting, a ribbon of 6 nanofibers is created into a nanofiber thread.

When viewed in detail, the ribbon 6 of nanofibers in the area of the virtual collector 7 oscillates due to the change in the polarity of the alternating electric voltage, the changes in the electric field caused by the changes in the electric wind and gravity. During each such movement, possibly uncompacted, i.e. insufficiently fixed or insufficiently entangled, nanofibers 5 stick to the surface of the ribbon 6 of nanofibers, from where they no longer separate due to the high specific surface area, mutual entanglement and intermolecular binding forces between individual nanofibers 5.

The weight of the ribbon of 6 nanofibers increases along its length, and thus the ratio of electric and gravitational forces changes. Therefore, for long spinning regions, or for several spinning regions that are repeated in succession and through which one ribbon of 6 nanofibers passes, a variable electric field is created by any of the known methods, for example by shielding the environment above the created ribbon of 6 nanofibers, or by shielding the spinning electrode 1 , or by variable shielding of the surroundings in the place above the created ribbon of 6 nanofibers. The goal is to adapt the intensity of the electric field to the variable weight of the ribbon of 6 nanofibers. So, for example, in places with a higher weight of the ribbon of 6 nanofibers, increase the intensity of the electric field.

The method of manufacturing the nanofiber thread consists in twisting the prepared ribbon of 6 nanofibers with either a false twist or a permanent twist. When twisting with a false twist, the ribbon of nanofibers 6 passes between two clamping points, between which a twisting device is placed, consisting of, for example, a twisting tube. The ribbon 6 of nanofibers is given a false twist by the twist device, which is twisted behind the twist device, while due to the high specific surface of the nanofibers 5 and the binding forces between the individual nanofibers 5, a relatively high degree of twist is preserved on the nanofiber thread as a residual twist.

The ribbon of nanofibers can also be subjected to a permanent twist.

Giving the twist to the 6 nanofiber ribbon can be done before winding it on the spool, following the production of the 6 nanofiber ribbon, or additionally by conventional methods, where the 6 nanofiber ribbon can be given a greater twist to achieve a higher strength of the produced thread, which will be even better processed by classic textile technologies on textile Ware.

Nanofiber threads and textile products made from them can serve as carriers of drugs or other biologically active substances for use in medicine and biomedicine, for example in the form of biological probes, skin covers, grafts, tissue carriers, so-called scaffolds, bandages, surgical and oral threads, etc. Furthermore, nanofibrous threads/yarns can be used for filter media, for example for the production of coil filters.

The device for carrying out the method described above, i.e. for the production of nanofibers 5 by alternating electric spinning of polymer solution Z for the production of a ribbon 6 of nanofibers, contains a spinning electrode 1, which in the first exemplary embodiment is formed by a thin rotating disk spinning electrode 11 with a horizontal axis of rotation placed in the lower part of its circumference in reservoir 2 of the polymer solution and coupled with a known rotary drive (not shown).

The disc spinning electrode 11 in the exemplary embodiment described below rotates around a horizontal axis and is connected to a source 3 of alternating high voltage, for example with an effective voltage value of 35 kV and a frequency of 50 Hz, and when it rotates, it carries out a polymer solution on its circumference. However, neither the rms voltage nor the frequency is limiting and other suitable values may be used. The vicinity of the free part of the circumference of the disc spinning electrode 11 in the spinning chamber 4 is called the spinning space 41, in which the spinning region 110 is formed on the spinning electrode 11. After supplying the spun polymer solution Z to the spinning region 110 on the free part of the circumference of the disc spinning electrode 11, spinning with alternating voltage will begin to form Taylor cones on the surface of the polymer solution in the central part of the spinning region 110,

- 9 CZ 2022 - 248 A3 from which the nanofibers 5 are elongated due to the effect of a strong electric field, which rise radially from the spinning region 110 from the circumference of the disk spinning electrode 11 and are carried by the electric wind in one plane formation away from the free part of its circumference in the direction of the maximum gradient of the generated electric fields, while in the area where the repeated natural slowing down to stopping of the nanofibers occurs, a virtual collector 7 is formed above the spinning area 110 around the circumference of the disk spinning electrode 11, i.e. the place where the nanofibers 5 are collected, compacted into a material structure and are pulled away in the form of a ribbon of 6 nanofibers.

The virtual collector 7 is formed in the place of the balance of the electric and gravitational forces acting on the formed nanofibers 5. The virtual collector 7 means the area around the disc spinning electrode 11, where the created nanofibers 5 lose their kinetic energy when moving from the surface of the disc spinning electrode 11. The reason their stopping is the reversal of the polarity of the disk spinning electrode 11 in every second half of the period of the supplied alternating electric voltage. The created nanofibers 5 remain with a residual electric charge of the polarity of the previous half-wave of electric voltage, so that they are now oppositely charged with respect to the current polarity of the disk spinning electrode 11. In this way, the electric potential difference necessary for the initialization and progress of the spinning process with an alternating electric voltage is created.

For a specific spinning solution, with a constant diameter of the disk spinning electrode 11 and a constant speed of its rotation, the place of creation of the virtual collector 7 can be influenced by the frequency of the supplied alternating voltage and its magnitude.

According to the technological requirements for spinning the processed polymer solution and the weight of the ribbon 6 nanofibers, the intensity E of the electric field can be changed by configuring the disc spinning electrode 11, i.e. by changing the diameter of the disc, the thickness of the disc, the relief of the surface of the peripheral part of the disc, by changing the speed and direction of rotation of the disc and of the pulling speed of the ribbon 6 of nanofibers from the virtual collector 7. However, care must be taken to ensure that the polymer solution Z does not dry on the circumference of the disk spinning electrode 11.

In the illustrated embodiment, the disc spinning electrode 11 rotates against the direction of pulling off the ribbon 6 of nanofibers. In this embodiment, there is a longitudinal orientation of the nanofibers 5 in the ribbon 6 and their partial parallelization, while by changing the ratio of the speed of rotation of the disk spinning electrode 11 and the withdrawal speed of the ribbon 6 of nanofibers, these properties can be changed according to the requirements for the further use of the ribbon 6 of nanofibers. The disk spinning electrode 11 can also be rotated in the same direction as the pulling direction of the ribbon 6 of nanofibers, in this case the parallelization of the nanofibers 5 in the ribbon 6 of nanofibers will be smaller and the nanofibers 5 will not be so longitudinally oriented.

As part of the verification of production possibilities, disc spinning electrodes with diameters up to 500 mm and thickness up to 5 mm were tested at rotation speeds from 10 to 30 min ^-1 . The alternating electric field was formed by an alternating voltage with an amplitude of 20 to 50 kV depending on the geometry and arrangement of the spinning electrode 1 at a frequency of 10 to 100 Hz. Polymer solution Z usually consists of a solution of PVB, PCL, PVA, or other polymer solutions spinnable in an alternating electric field.

The thin rotating disc spinning electrode 11 is shown in section in Fig. 1b and 2a, and in view of Fig. 3, from which it is clear that the nanofibers 5 formed on the periphery of the electrode 11 are carried away from it in the radial direction, i.e. perpendicular to its axis of rotation in the direction of the maximum electric force gradient, which is shown by the arrow.

In Fig. 2b shows a cross-section of a rotating disk spinning electrode 11 with a greater thickness, for example 6 mm, where one spinning area 110 is formed on each edge of the disk spinning electrode 11, in which Taylor cones are formed. In view, this electrode is shown in Fig. 4. Nanofibers 5 are created on both edges and due to the effect of the electric wind, they are carried away from them in the direction of the maximum values of the electric field gradient, which are

- 10 CZ 2022 - 248 A3 shown by arrows, and create two conical flat formations that move away from each other, as shown in Fig. 4. In addition, the nanofibers 5 produced at both edges of the disc spinning electrode 11 have the same residual electrical potential, so they tend to repel each other and not connect to each other, further aiding the distance of the two conical planar formations. From the section in Fig. 2b and from the view of Fig. 4, it is clear that the nanofibers 5 are carried away from the disk spinning electrode 11 in the shape of the letter "V", while their path is perpendicular to the surface of the polymer solution in the area of the formation of nanofibers. The nanofibers 5 are therefore not carried away from the surface of the disk spinning electrode 11 in planar flat formations, but in two conical flat formations that move away from each other in the direction from the surface of the disk spinning electrode 11, so that the mutual distance of the virtual collectors 7 is greater than the thickness of the disk spinning electrode 11, as shown in FIG. 4. In addition, the gravitational force acts on the nanofibers 5, which deforms the conical surface formations, so that the virtual collector 7 is formed under the surface of the electric field gradient. Both ribbons 6 of nanofibers produced in virtual collectors 7 have the same properties as described above and can be further wound separately, or bundled and wound together, or brought to a device for the production of nanofiber yarn, which will be described later.

The wide disc spinning electrode 11 can be further improved by forming a recess 111 in the middle of the peripheral surface, so that the edges of the peripheral surface adjacent to the faces form protrusions 112 on which the intensity E of the electric field is concentrated, thereby creating two spinning regions 110. to the fact that the intensity E of the electric field is concentrated on the protrusions 112, so compared to the previous embodiment of the wide disk spinning electrode 11, the spinning regions 110 with a supercritical electric field intensity are narrowed. Even in this embodiment, the nanofibers 5 are carried away from the surface of the disk spinning electrode 11 in two conical planar formations in the direction of the maximum gradients of electrical forces, which are shown by arrows. The conical surface formations move away from each other in the direction of the surface of the disk spinning electrode 11, so that the mutual distance of the virtual collectors 7 is greater than the thickness of the disk spinning electrode 11. This is also helped by the repulsive forces between the equally charged nanofibers 5. In addition, the nanofibers 5 are affected by the force of gravity, which deforms the conical surface formations so that the virtual collector 7 is formed under the surface of the electric field gradient. Both ribbons 6 of nanofibers have the same properties as described above and can be further wound separately, or bundled and wound together, or fed into a nanofiber yarn production device, which will be described later.

Another alternative arrangement of the device for the production of a ribbon of 6 nanofibers is shown in Fig. 5, where two disk spinning electrodes 11 are arranged on a common shaft. Each of the disk spinning electrodes 11 works the same as a separate disk spinning electrode 11, as shown in FIG. 1 and described above. The device produces two ribbons of 6 nanofibers that can be wound individually or bundled and wound together. It is clear from the arrangement shown that the number of disc spinning electrodes 11 can be greater.

In this embodiment, a different polymer solution can be used for each disc spinning electrode 11, so that after joining the manufactured ribbons 6 of nanofibers, a component nanofiber thread is formed, formed from nanofibers 5 of two or more different polymers.

To produce a single ribbon 6 of nanofibers with a higher specific gravity, the disc spinning electrodes 11 can be arranged one behind the other, as shown in Fig. 6a in elevation and in Fig. 6b in plan view, showing three disk spinning electrodes 11a, 11b, 11c, each of which operates in the same way as a separate disk spinning electrode 11 as shown in FIG. 1b, 2a and Fig. 3 and described above. In particular, due to the shortening of the length of the spinning device, the disk spinning electrodes 11a, 11b, 11c are partially offset from each other, so that in the front view, the second disk spinning electrode 11b overlaps the front part of its circuit with the rear part of the circuit of the first disk spinning electrode 11a and with its rear part it overlaps the front part of the circuit third disc spinning electrodes 11c. By mutual displacement of the disk spinning electrodes 11a, 11b, 11c, the sagging of the ribbon 6 of nanofibers between the disk spinning electrodes 11a, 11b, 11c is reduced. Spinning takes place in the upper part of the individual disc spinning electrodes 11a, 11b, 11c,

- 11 CZ 2022 - 248 A3 while the ribbon 6 of nanofibers is pulled from the first disk spinning electrode 11a through the second disk spinning electrode 11b and the third disk spinning electrode 11c to be wound on a spool or for further processing. Increasing the intensity of the electric field along the length of the pulled ribbon 6 of nanofibers is achieved, for example, by reducing the thickness of successive disk spinning electrodes 11a, 11b, 11c, or by adjusting the high alternating voltage on the individual disk spinning electrodes.

Another alternative of the device for the production of the ribbon 6 of nanofibers by alternating electrospinning is the device with the strip spinning electrode 12 shown in Fig. 7a, 7b. The device contains a reservoir 2 of a polymer solution, into which the lower part of its circumference reaches the rewinding shaft 8 coupled to the drive 81. Above the rewinding shaft 81, in the spinning chamber 4 on the frame of the device, a blade 121 is firmly fixed, for example by means of struts 82. The rewinding shaft 81 is together with edge 121 girded by an endless belt 122, which emerges from the polymer solution 21 and bends over the winding shaft 8 over the edge 121. The belt 122 carries the polymer solution Z from the reservoir 2, and the bend of the belt 122 forms the spinning area 120 of the belt spinning electrode 12, which is connected to sources of alternating electrical voltage. An alternating electric voltage can be supplied to the polymer solution Z in the reservoir 2, or to the edge 121. Taylor cones are formed on the spinning area 120 of the strip spinning electrode 12, from which the nanofibers 5 are elongated, which are carried upwards to the virtual collector by the effect of the electric wind 7, while they move through the spinning space 41 in one planar surface formation. In the place of the virtual collector 7, the nanofibers 5 are collected and compacted into a material formation forming a ribbon 6 of nanofibers, which is pulled from the virtual collector 7 in a known manner, not shown in detail, and wound on a coil, or is brought to a device for the production of a nanofiber thread, which will be described later .

Similar to the disk spinning electrode 11, the width of the edge 122 can be larger, so that on the wide strip spinning electrode 12, two spinning regions 120 on both of its edges, on which Taylor cones are formed, and the nanofibers 5 are entrained from the spinning regions 120 in the direction of the maximum gradient electric fields, namely in two planar flat formations that create the letter "V" in cross-section, to the regions of virtual collectors 7, the mutual distance of which is greater than the width of the edge 122 of the strip spinning electrode 12. In this device, two ribbons 6 of nanofibers are created , which have the same properties and can be further wound separately, or they can be grouped together and wound together, or they can be fed to the thread production equipment. This embodiment is not shown. The conical surfaces will be deformed by the action of gravity as in the previous cases.

Another alternative of the device for the production of the ribbon 6 of nanofibers by alternating electrospinning is the device with the overflow spinning electrode 13 shown in Fig. 8a, 8b. The device contains a reservoir 2 of polymer solution Z, in which a supply 131 of polymer solution Z is vertically placed. An overflow electrode 13 is arranged at the upper end of the supply 131 of the polymer solution, while the supply 131 opens at its upper end. An overflow surface 132 is formed around the mouth of the polymer solution supply 131, which slopes slightly from the mouth of the polymer solution supply 131 to the edge of the overflow electrode 13 and ends with a peripheral edge 133, on which Taylor cones are formed, from which nanofibers 5 are elongated, which due to the effect of electric wind, they are carried by the spinning space 41 in the radial direction from the peripheral edge 133 of the overflow electrode 13 and are collected at the place of the virtual collector 7, where they are compacted into a material structure forming a ribbon 6 of nanofibers, which is pulled away from the virtual collector 7 in a tangential direction and further wound on a spool (not shown) or processed into thread. The virtual collector 7 is actually formed at the point of balance of electric and gravitational forces, while the force of the electric wind from the inlet 131 of the polymer solution Z is also acting upwards, so that a conical planar structure directed upwards is formed. In addition, this formation is deformed by the action of gravitational force.

Another alternative of the device for producing a ribbon 6 of nanofibers by alternating electrospinning is a device in which the linear spinning electrode 14 is formed by an endless linear flexible structure, which in the first embodiment is placed on two rotatably placed coils 141 coupled to a drive (not shown). At least one of the coils 141 extends part of its circumference into the magazine 2

- 12 CZ 2022 - 248 A3 of polymer solution Z. In the embodiment shown, each coil 141 has its own reservoir 2 of polymer solution.

The linear flexible structure forming the linear spinning electrode 14 can be formed, for example, by a string, a tape, a strap, or a structure with a more fragmented surface composed of several mutually intertwined or intertwined parts, such as a cable, a cord, a multi-core structure, etc. As in the previous embodiments, on the linear spinning electrode 14 creates a spinning region 140 of finite length which is open in the spinning direction. In the central part of the spinning region 140, a narrow flat formation of the polymer solution Z is formed, and the intensity E of the electric field is set to a supercritical value, at which the nanofibers 5 are formed. The nanofibers 5 move from the spinning region 140 in the flat formation in the direction of the maximum gradient of electric forces, in the embodiment shown, i.e. in a vertical plane. The nanofibers 5 gradually lose their kinetic energy, and in a place with zero kinetic energy, the nanofibers 5 create a linear virtual collector 7, in which the nanofibers 5 stop, collect and compact into a ribbon 6 of nanofibers. The linear flexible structure forming the linear spinning electrode 14 is endless and is designed according to Fig. 9 is placed on two coils 141, which can be seen by grooves for temporary placement of the linear spinning electrode 14, while the dimensions and shape of the cross-section of the groove corresponds to the size and shape of the linear spinning electrode 14. The coils 141 are placed with part of their circumference in the polymer solution Z. The linear spinning section electrodes 14 between the coils 141, form the spinning region 140. In the embodiment of the linear spinning electrode 14, in which the polymer solution Z is in the spinning region 140 on the entire circumference of the linear spinning electrode 14, as shown in Fig. 9c, a shielding bar 142 is arranged under the spinning area 140, which prevents the creation of a supercritical value E of the electric field outside the upper part of the linear spinning electrode 14, so that in some cases the shielding bar 142 also surrounds the side parts of the linear spinning electrode 14. All the created nanofibers 5 are then created especially in the middle of the spinning area 140, which is a straight line, and are carried upward from the spinning area 140 in the direction of the maximum gradient of the electric field in a planar planar structure in the vertical direction, while gradually losing their kinetic energy, and at a place with zero kinetic energy, the nanofibers 5 form a linear virtual the collector 7, in which the nanofibers 5 stop, collect and compact into a linear ribbon 6 of nanofibers, which is pulled away.

In Fig. 10a, 10b, the linear spinning electrode 14 is also formed by an endless linear flexible structure. In this embodiment, one common reservoir 2 of the polymer solution is used, into which both rollers 141 extend with a part of its circumference, the linear spinning electrode 14 moves in one direction and at the end of the spinning area 140 it surrounds the return roller 141 and returns back to the reservoir 2 of the polymer solution and via the delivery roller 141 it comes again to the spinning area 140. Even in this embodiment, a shielding bar 142 can be used for some linear flexible formations. The part described above applies to the linear spinning electrodes 14 formed by narrow linear flexible formations on which the polymer solution Z is applied to their entire circumference.

In the design according to Fig. 11, the linear spinning electrode 14 is formed by a wide strip 143, in the central part of which a recess 1431 is formed, which creates protrusions 1432 on the edges of the strip, on which, similarly to the embodiment according to Fig. 2c creates spinning regions. From both spinning regions 140, the nanofibers are entrained in the direction of the maximum gradient of the electric fields, namely in two flat planar formations that form the letter "V" in cross-section, to the regions of virtual collectors 7, the mutual distance of which is greater than the distance of the protrusions 1432. U of this device, two ribbons of 6 nanofibers are created that have the same properties and can be further wound separately, or they can be bundled and wound together, or they can be fed into a thread production device.

In the embodiment according to Fig. 12, the linear spinning electrode 14 is formed by a flat strip 144, of which the spinning regions are formed on its edges 1441. Since the thickness of the strip 144 is small compared to its width, the maximum gradient of the electric field is directed from the edges of the strip to the sides. Another reason is the fact that the environment above and below the flat 144 tape is

- 13 CZ 2022 - 248 A3 the same, so it does not catch up to the deviation of the maximum gradient of the electric field. In this way, two planar surface structures are created from the produced nanofibers, which end in the corresponding virtual collectors, not shown, where two ribbons of nanofibers are created, which are pulled away in the same way as in the previous embodiments. Due to the action of gravitational forces, planar surface formations will be deformed by these forces, just like in other designs.

An apparatus for the continuous production of a nanofibrous thread 60 from a ribbon of nanofibers 6 will be explained and described in combination with a rotating disc spinning electrode 11 for the production of a ribbon of nanofibers 6, as shown in FIG. 13. The ribbon 6 of nanofibers is led from the virtual collector 7 of the disk spinning electrode 11 to the device 9 for the production of nanofiber thread 60, which in the illustrated embodiment contains a transfer roller 91 behind which the first withdrawal device 92 of the ribbon 6 nanofibers is arranged in the direction of movement of the ribbon 6 of nanofibers . A twisting device 93 for creating a false twist is arranged behind the first take-off device of the nanofiber ribbon 6, behind which there is a second take-off device 94, behind which a drying and/or fixing unit 95 is included, behind which there is a third take-off device 96, behind which there is a winding device 97.

The ribbon 6 of nanofibers is pulled from the virtual collector 7 of the disk spinning electrode 11 via the transfer roller 91 by the first pull-off device 92 and enters the twisting device 93, in which it passes through the twisting member 931, for example a cruel tube, which gives it a wrong twist. From the twisting device 93, the twisted ribbon 6 of nanofibers is removed by the second withdrawal device 94. The twist is given to the ribbon 6 of nanofibers by the twisting member 931 of the twisting device 93 between two clamping points formed by the first withdrawal device 92 and the second withdrawal device 94. Between the first withdrawal device 92 and the twisting device the twist is created by the device 93 and between the twist device 93 and the second pull-off device 94 the twist is untwisted, while due to the high specific surface of the nanofibers 5 and the binding forces between the individual nanofibers 5, a relatively high degree of twist is retained as a residual twist even after untwisting, which creates nanofibrous thread 60. The nanofibrous thread 60 is removed from the second exhaust device 94 by the third exhaust device 96 through the drying and/or fixing unit 95, in which the solvent residue is evaporated and, if necessary, the nanofibrous thread 60 is thermally fixed. From the third take-off device 96, the nanofibrous thread 60 is led to the winding device 97, in which it is wound onto a spool by some of the known methods.

At the same time, the ribbon of nanofibers can be produced on any of the devices described above.

The device 9 for producing the nanofibrous thread 60 from the ribbon 6 of nanofibers can also be arranged in another suitable way, for example it can include a device for creating a permanent twist.

Or, the production of the nanofiber thread from the nanofiber ribbon can be carried out on a special device from the nanofiber ribbon wound on a spool in another operation.

Industrial applicability

With the method of producing nanofibers by alternating spinning according to the invention, a sufficient amount of nanofibers can be produced and a ribbon of nanofibers can be created from them, which is capable of being pulled off and wound onto a spool, while also being able to be unwound from the spool for the purpose of its use or further processing.

Claims (26)

1. A method of producing nanofibers by alternating electrospinning of a polymer solution or melt on the spinning electrode (1), in which the nanofibers (5) are formed from the polymer solution (Z) or polymer melt in the spinning region (10) formed on the spinning electrode (1) and driven by the electric wind, they are carried away from it, characterized by the fact that in the spinning region (10) a narrow planar linear formation of polymer solution or melt is formed, which has a finite length and is open in the direction of spinning, and in the spinning region (10) length will create a supercritical intensity (E) of the electric field, at which nanofibers (5) are formed, which move from the spinning region (10) in a planar formation, in which they gradually lose their kinetic energy and form nanofibers in a place with zero kinetic energy ( 5) linear virtual collector (7), in which nanofibers and (5) stop, collect and compact into a linear nanofiber formation, the so-called ribbon (6) of nanofibers, which is pulled away. 2. The method of producing nanofibers by alternating electrospinning according to claim 1, characterized in that the virtual collector (7) is formed at the point of force balance of all electrical and gravitational forces acting on the created nanofibers (5). 3. The method of producing nanofibers by alternating electrospinning according to claim 1 or 2, characterized in that the spinning region (120) is straight and the nanofibers (5) emerging from it move in a planar surface formation. 4. A method of producing nanofibers by alternating electrospinning according to claim 1 or 2, characterized in that the spinning area (110) is formed by a part of a circle on the circumference of the disc spinning electrode (11) and the nanofibers (5) emerging from it move in a planar plane perpendicular to on the axis of rotation of the disc spinning electrode (11), while the linear virtual collector (7) is formed by part of a circle. 5. The method of producing nanofibers by alternating electrospinning according to claim 3, characterized in that two spinning regions (120) are formed near the edges of the spinning electrode (11), in which the nanofibers (5) are formed in the direction of the maximum values of the electric field gradient, whereby the nanofibers (5) emanating from both spinning regions (120) move in conical flat formations that move away from each other in the direction of movement of the nanofibers (5). 6. A method of producing nanofibers by alternating electrospinning according to claim 4, characterized in that two spinning regions (110) are formed near the edges of the peripheral surface of the disk spinning electrode (11), in which nanofibers (5) are formed in the direction of the maximum values of the gradient electric field, while the nanofibers (5) coming from both spinning areas (110) move in conical flat formations that move away from each other in the direction of movement of the nanofibers (5). 7. A method of producing nanofibers by alternating electrospinning according to any one of the preceding claims, characterized in that the withdrawn ribbon (6) of nanofibers is wound on a spool in a winding device (96). 8. The method of producing nanofibers by alternating electrospinning according to claim 7, characterized in that the pulled ribbon (6) of nanofibers is given a twist before winding. - 15 CZ 2022 - 248 A3 9. The method of producing nanofibers by alternating electrospinning according to claim 8, characterized in that the drawn ribbon (6) of nanofibers is given a false twist. 10. The method of producing nanofibers by alternating electrospinning according to claim 8, characterized in that the withdrawn ribbon (6) of nanofibers is given a permanent twist. 11. A device for the production of nanofibers by alternating electrical spinning of a polymer solution or melt according to one of the preceding claims, in which a spinning region (10, 110, 120, 130, 140), characterized by the fact that on the spinning area (10, 110, 120, 130, 140) of the spinning electrode (1, 11, 12, 13, 14) there is a flat linear formation of polymer solution or polymer melt , which has a finite length and is open in the direction of spinning, i.e. in the direction of the maximum gradient of the electric field, while a supercritical intensity (E) of the electric field is created over the entire length of the spinning region (10, 110, 120, 130, 140), at which nanofibers (5) are formed, which are carried in the direction of the maximum gradient of the electric field in a planar formation into the linear virtual collector (7), where they are stopped and compacted into a ribbon (6) of nanofibers, which leads them to the withdrawing and winding device. 12. Device according to claim 11, characterized in that the spinning area (120, 140) of the spinning electrode (12, 14) is straight. 13. Device according to claim 12, characterized in that the spinning electrode is formed by a strip spinning electrode (12) and the maximum gradient of the electric field is directed vertically upwards. 14. Device according to claim 12, characterized in that the spinning electrode is formed by a linear spinning electrode (14) formed by a linear flexible structure. 15. Device according to claim 14, characterized in that the linear flexible structure is a cable, not a thin strip or a thin strap. 16. Device according to claim 14 or 15, characterized in that the linear flexible structure forming the spinning electrode (14) is a structure composed of several mutually intertwined or intertwined parts, while a shielding bar (142) is arranged under the spinning area (140). 17. Device according to claims 12- 14, characterized in that two spinning regions (10, 120, 140) are formed on the spinning electrode (1, 12, 14) near its edges. 18. Device according to claim 17, characterized in that projections (1432) are created on the edges of the linear flexible structure t formed by the belt, on which the maximum gradient of the electric field is concentrated. 19. Device according to claim 17, characterized in that the linear flexible structure is a flat strip and the fibering region (140) is formed at its edges, with the maximum gradient of the electric field directed from the edges of the strip to the sides in a horizontal direction. - 16 CZ 2022 - 248 A3 20. The device according to claim 11, characterized in that the spinning electrode is formed by a narrow rotating disc spinning electrode (11), which with the lower part of its circumference extends into the polymer solution (Z) or melt in the reservoir (2) and on the free part of the disc circumference of the spinning electrodes (11), a spinning region (110) is formed, which is formed by a part of a circle, while the maximum gradient of the electric field is directed from the spinning region (110) in the radial direction, and the nanofibers (5) are entrained in a planar surface formation from which a ribbon (6) of nan fibers is formed in the virtual collector (7). 21. Device according to claim 20, characterized in that the rotating disk spinning electrode (11) is mounted on a common shaft with at least one other rotating disk spinning electrode (11). 22. Device according to claim 21, characterized in that for each of the rotating disk spinning electrodes (11) there is a solution of a different polymer in the reservoir (2) of the polymer solution. 23. Device according to claim 20, characterized in that behind the first rotating disc spinning electrode (11) in the direction of formation and removal of the ribbon (6) of nanofibers, at least one other disc spinning electrode (11) is placed. 24. Device according to claim 11, characterized in that the rotating spinning disk electrode (11) has a larger width, so that two spinning regions (110) are formed on its edges, which are formed by a part of a circle and the maximum gradient of the electric field is created on both edges disk spinning electrodes (11) conical surface formations in which nanofibers (5) are carried into virtual collectors (7) in which a ribbon (6) of nanofibers is formed, while the conical surface formations of nanofibers (5) move away from each other and they form the letter "V" in cross-section. 25. The device according to claim 11, characterized in that the spinning electrode is formed by an overflow spinning electrode (13), while the device contains a reservoir (2) of polymer solution (Z), in which the supply (131) of polymer solution (Z) is placed vertically , at the upper end of which an overflow electrode (13) is arranged, while the inlet (131) opens on its upper face and an overflow surface (132) is formed around its mouth, which slopes slightly from the mouth of the inlet (131) of the polymer solution to the edge overflow electrode (13) and is terminated by a peripheral edge (133), which forms the spinning area (130) of the overflow spinning electrode (13), on which the nanofibers (5) are elongated, which are carried by the spinner due to the effect of the electric wind in the direction of the maximum electric field gradient through the space (41) in the radial direction from the peripheral edge (133) of the overflow electrode (13) and are collected at the point of the virtual collector (7), where they are compacted into a material formation forming a ribbon (6) of nanofibers, which is from the virtual collector (7) drawn off in a tangential direction to the virtual collector (7) and further wound onto a coil or processed into a thread. 26. Device for the production of nanofibrous thread, characterized in that the ribbon (6) of nanofibers is led from the spinning device to the device (9) for the production of nanofibrous thread, which contains a twisting means for creating a false or permanent twist and is subsequently led into the winding device .